1. Field of Invention:
This invention relates to window insulation and specifically to an exteriorly applied retractable, flexible, insulating glazed surface covering (hereinafter referred to as a curtain) which operates from the interior of the building.
2. Discussion of the Prior Art:
Heretofore, window insulation systems for protecting a living space from massive thermal exchange at windows during heating and cooling seasons have been principally located in the interior of the building. Such systems are commonly constructed from materials, including cloth, paper and plastic. They can function in tracks or hang free and they may be insulated or uninsulated. Rolled curtains and Roman shades with various devices and materials to allow sealing at the perimeter and for storing the curtain when not in use, represent two of the most common types of construction.
A primary problem, however, that arises with the use of interiorly mounted curtains is that it is difficult to provide a perfect seal between the curtain and window against convection. Convection of heated, humid interior air to the glazed surface, which has a temperature that is much cooler than the ambient room air, results in condensation and frost buildup when the curtains are closed. Upon opening such a curtain or shade and exposing the window to sunlight, the frost melts rapidly. What results is a mess, damaging the window sills, walls, floors, and carpet. Additionally, water borne films rapidly develop on the glass. This filming requires constant cleaning if one intends to sustain passive solar efficiency. Furthermore, windows having interiorly mounted curtains are more likely to break from thermal shock.
Available curtain systems also have other drawbacks. One is storage, namely, where and how does one store these devices. A second problem arises with the decor, since they frequently have their own designs which can be aesthetically unpleasant. They also present handling problems in that they are bulky and, in exceptional circumstances, children, handicapped or elderly persons may have great difficulty in operating these devices.
Exteriorly mounted insulating systems, on the other hand, are inherently free of condensation, since they allow the innermost glass to warm to a temperature which is close to the ambient interior temperature. Various systems have been tried. On the market are the Solaroll.TM. and the Pease Rolling Shutter .TM. systems. These systems provide an R (resistance factor) rating of nearly 1, which is minimal. These two systems are chiefly designed to provide security, as claimed in their own advertising literature. Canvas, Roman shades, rollup shades and other coverings held with grommets have also been tried on the exterior, each again having a very low R rating. Another layer of transparent material may be added over the glazed surface, such as Mylar.TM., Plexiglass.TM., vinyl or glass, again with a very low R. Finally, rigid insulation can be placed over the exterior of the glazed surface by hand, nailed, bolted, placed on hinges or in tracks.
Currently, the best exterior window insulation is provided by permanently covering the window with a rigid insulation covered with a reflective surface. Its major drawbacks are its appearance, and the difficulties encountered upon attempting to remove them. The window becomes a wall, allowing for no light to enter the living area and for no one to look out.
Movable rigid metallized foam placed on tracks or hinges are next best, but they are difficult to seal. They also require a place for storage when not in use, which is rarely available on the exterior walls of buildings, and which is also unsightly in the daylight hours. Storing this type of insulation on the exterior of the building also requires one to cover and uncover the windows twice a day, regardless of weather conditions. These rigid systems also allow some convection and conduction loss because they are not air tight. Still further, they are easily breakable and can be dangerous to handle in a wind.
Exterior canvas applications provide little protection from conduction, convection and radiant heat loss. Mylar or other translucent films allied permanently to the glazed surface add very little to conduction resistance, and while they may reduce convection losses, they do not alter radiant losses. In addition, they can distort the view and reduce solar gain. Plexiglass and glass also reduce solar gain.
In summary, the major disadvantages of interior insulating window systems are storage space, insufficient area to move the insulation to the storage position, decor and condensation problems, with resultant water damage. The major disadvantages of exterior insulating window systems as grouped by material are that films, glass, plexiglas and canvas are ineffective regarding prevention of heat loss and provide no security. Foam and other rigid insulating materials, on the other hand, present storage and other handling problems because they must be removed by hand from the exterior of the building under all weather conditions. The Pease and Solaroll systems, in turn, have little insulating value and are expensive beyond they insulating worth, as well as being subject to breakage.
Accordingly, several objects of our invention are that it mount to the outside of the structure and that it be sealable, movable and retractable. Other objects are that it present a high resistance to thermal transfer from conduction, convection and radiation. In particular, these objects are achieved in a curtain that is operable from inside the building. In its covering position it is sealed at the sides by tracks in which it glides and at the top and bottom by contact-type seals. When the sun shines, solar energy can thus be collected in the building by either pulling an activating rope, turning a crank or throwing a switch so as to uncover the window and roll the curtain into its storage position, with no problems of condensation on either glazed surface of the window. The curtain stays in the storage position indefinitely, or until its insulating properties are again required.
Still other objects, advantages, and distinctions of our invention, as well as its construction, will become apparent from a consideration of the drawings and ensuing description thereof.